Peritalar Configuration Following Fusion in Varus Ankle Osteoarthritis: A 3D Weight Bearing CT Analysis

Abstract

Category: Ankle Arthritis; Ankle Introduction/Purpose: In varus-type osteoarthritis of the ankle (VAOA), it is known that the subtalar joint compensates in valgus/eversion for the malalignment of the tibiotalar joint. However, previous studies were mainly based on X-ray measurements and did not take into account peri-talar changes that extend to the subtalar and Chopart joints. Furthermore, the effect on peritalar compensation when tibio-talar arthrodesis is performed is still unclear. Distance Mapping (DM) is a technology that can produce a 3D point-to-point distance map of joint interactions from cone beam weight bearing CT (WBCT) images. The purpose of this study was to quantify the peri-talar changes that occur when the tibiotalar joint is fused. We hypothesized that talar varus would improve and that the Chopart/Subtalar joint complex would present compensatory varus/inversion. Methods: The subjects were 14 patients (15 feet) who underwent arthrodesis for VAOA at our institution. The average postoperative follow-up period was 6.6 months. Foot alignment (Foot Ankle Offset (FAO)) was measured from WBCT datasets pre and postoperatively. The pre to post op shift vectors of the weighted distance maps center points were measured for the tibiotalar, subtalar, calcaneocuboid and talonavicular joints. Statistical analysis was performed by paired T-test, and the significance level set at p<0.05. Results: FAO improved significantly from preoperative -12.9 +-7.4 % to postoperative -6.4 +-3.9 %. The DM vectors were 4.9 +-2.8 mm (lateral direction) for the tibiotalar joint, 0.86 +-0.93 mm (posterior) for the subtalar joint and 4.9 +-2.6 mm (plantar- medial) for the talonavicular joint. Conclusion: The main finding in this study was that foot alignment was improved following tibiotalar arthrodesis with peritalar compensation, more so in the talonavicular than in the subtalar joint and not in the calcaneocuboid joint. The limitations of this study include the small number of cases and the short postoperative follow-up. Our results suggest that the flexibility of the talonavicular joint may be necessary when arthrodesis is performed on VAOA to contribute to the alignment correction. If it is not the case, TAR could be considered an alternative.